Effect of ammonium ion on morphogenesis from cultured cotyledon explants ofPanax ginseng

Cotyledon expiants ofPanax ginseng were cultured on modified Murashige and Skoog medium with various concentrations of NH₄C1 and KNO,. Morphogenesis such as somatic embryo, embryogenic callus, or adventitious root formation from cotyledon expiants differently occurred according to the concentrations of NH/ and NO₃. Somatic embryos were actively formed in a moderate concentration of NH₄ ⁺ (20 mM) in combination of NO₃, but in a high concentration of NH₄ ⁺ (60 mM), only embryogenie calli were formed. In little or no NH₄ ⁺, adventitious roots were formed at a high rate. The influence of NO₃ on those morphogenesis was slight but combination of NO₃ with NH₄ ⁺ was indispensable since the cotyledon expiants were necrotized on medium containing only NH₄ ⁺ as a nitrogen source. Histological observation revealed that somatic embryo and embryogénie callus formation occurred from the same origin (cotyledon epidermis), whereas, adventitious roots were originated from the cells near vascular strands.